Carrier and modulation indicator



Dec. 27, 1938. J. L. REINARTZ 2,141,668

CARRIER AND MODULATION INDICATOR Filed Dec. 29, 1956 INVENTOR JOHN L. RE! NARTZ Patented Dec. 27, 1938 UNHT STAT GFFIE CARRIER AND MODULATION INDICATOR Delaware Application December 29, 1936, Serial No. 118,048

3 Claims.

My invention relates to visual indicating means for quantitatively analyzing carrier waves and percentage modulation.

The modulated carrier wave of a radio transmitter is usually monitored by a complicated and expensive voltmeter of the vacuum tube or cathode ray oscillograph type, which is impractical for use with many short wave transmitters.

It is an object of my invention to provide an improved visual monitoring device for use as an indicator of the energy level of a carrier wave and its percentage modulation.

One element of my improved indicator comprises a cathode ray tube commercially known in the trade as a tuning indicator, one form of which is sold on the market as radio tube type 6E5, and is described in U. S. Patent 2,051,189 to H. M. Wagner. This particular visual indicator comprises a straight thermionic cathode around one section of which is positioned the electrodes of a triode comprising a grid and an anode, and around another section of which is mounted a conical shaped electrode or target coated on its concave surface facing the cathode with a material that lights with a fluorescent or glow when bombarded with electrons. A deflecting electrode comprising a flattened wire placed parallel to the cathode between the target and cathode so shields the target from electron bombardment that a shadow divides the lighted surface of the glowing target by a dark fanshaped area, the size of the area being proportional to the negative potential on the deflecting electrode. This electrode is connected directly to the anode in the triode section. The voltage developed by the space current of the triode section flowing through an impedance connected to the anode is impressed between the deflecting electrode and the fluorescent target to change the light pattern in response to changes in potential on the grid of the triode section. The grid is commonly connected to a source of direct current potential in a radio receiving circuit which changes in value in response to the resonant condition of the receiver to indicate its tuning.

According to my invention, I provide circuits for impressing the carrier, with or without modulations, directly on the grid and cathode of the visual indicator tube. The carrier is rectified in the grid circuit causing the grid bias to assume a value proportional to the amplitude of the carrier. The resulting light patterrron the fluorescent target becomes a function of the carrier level. Signal modulation of the carrier causes the fluctuate in potential and the light or to pattern to change, the percentage change in the dark area being proportional to percentage modulation. With my improved device, the carrier level and the percentage modulation of the carrier are readily and visually determined.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing.

A form of visual indicator such as that shown in the Wagner Patent 2,051,189 comprises an envelope I, an indirectly heated cathode 2 with electron emitting surfaces 3 and 4, grid 5, anode 6, fluorescent target or plate I, and electron deflection electrode 8 connected directly to anode 6. A source of potential 9, shown by way of example as a direct current source, is connected to the anode through impedance Ill, the fluorescent target being connected to the impedance so that the voltage produced across the impedance by the anode-cathode space current is impressed upon the target. Impedance l0 may be bypassed with an R. F. condenser. The value of the space current and the corresponding deflection of electrons projected toward the fluorescent target are controlled by grid 5.

One modulation indicator constructed according to my invention comprises a tank circuit with parallel inductance l l and tuning condenser 42 directly connected at one end to grid 5 and at its other end to the adjustable contact on resistance potentiometer l3 which is connected at its ends to the cathode and to the negative side of the plate current supply. The two portions of the resistance on either side of the contact is designated as M and I5. Condenser l6, having a low carrier frequency impedance, is connected between. the cathode and the sliding contact of the potentiometer, while condenser ll, having a low signal frequency impedance, is connected between the sliding contact and the outer end of the potentiometer.

In operation, a carrier wave with or without modulations is picked up preferably by an antenna l8 and fed through a conventional coupling coil 19 to the tank circuit which, when tuned to resonate with the incoming carrier, impresses the high frequency wave upon the cathode and grid of the tube. The carrier is rectified by the grid and cathode as in a conventional diode and charges radio frequency condenser Hi to substantially the peak value of the impressed carrier wave. For a steady unmodulated carrier wave,

condenser it will assume a fixed charge impress ing upon the grid a steady negative biasing potential. The resulting steady anode-cathode space current develops a direct current potential across impedance i0 causing a predetermined bias upon deflection electrode 8 and a steady light pattern of fixed dark area on target 7. With no signal or carrier wave, the contact of the potentiometer may conveniently be adjusted to make the dark area on the target of a predetermined size, so that when a carrier of unknown amplitude is impressed upon the grid with a corre sponding diminution of the dark area on the target, the potentiometer contact may be readjusted to again reproduce the original dark area, thus obtaining a quantitative measure of the carrier level. Markings may conveniently be placed upon the potentiometer adjusting knob and the circuits calibrated so that accurate measurements of any unknown carrier energy may be made.

A modulated carrier wave impressed upon the input electrodes of my novel indicating device will cause the charge on condenser it to fluctuate in value following the envelope of the peaks of the high frequency wave and to impress a corresponding varying potential upon the grid. The anode-cathode space current and the voltage across impedance IE will vary in accordance with those signal modulations, Will vary the bias upon deflecting electrode 8 and cause a corresponding variation in size of the dark area on the target. A visual indication is thus obtained of the signal modulations on the carrier wave.

To monitor modulations on the carrier, according to one method of operating my device, the dark area of the light pattern may be adjusted by the potentiometer to maximum or some intermediate value, when no carrier is applied to the input electrodes. The strength of an unmodulated carrier in the tank circuit is then adjusted until the dark area is one-half said intermediate value. Then, upon modulating the carrier, the dark area flickers in width indicating the presence of the modulations, modulation serving to reduce the dark area to zero. Modulation in excess of 100% causes an overlap of the light area of the pattern which is readily detected as a bright line opposite electrode 8.

The modulation indicator constructed according to my invention is inexpensive, simple to operate, and is particularly flexible in use. The indicator, as described, may be inexpensively manufactured from the few elements shown and may be conveniently set up adjacent a transmitter for quantitatively measuring carrier strength and monitoring signal modulations on the carrier. Good results have been obtained by using, in connection with a commercial 6E5 type tube, a

50,000 ohm potentiometer at l3, a one megohm resistor at I0, and about 100 m. m. f. and .10 m. f. condensers at E6 and I7 respectively.

While I have indicated one embodiment of my invention, and have described one preferred application thereof, it will be apparent that my'invention is not limited to the exact form illustrated or to the use indicated, but that many variations may be made in the particular circuits used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is-- 1. A visual modulated carried monitoring device comprising an envelope containing a cathode having two emitting sections, a grid and anode surrounding one of said sections, a plate adjacent the other of said sections coated with material that fluoresces with electron bombardment, and an electron deflecting electrode between said other emitting section of said cathode and the coated plate and electrically connected to the anode, a resonant high frequency circuit connected at one end to said grid, an impedance connecting said anode and plate, a high voltage source of potential connected to said plate, a potentiometer connected between said cathode and the negative end of said source, a connection between an adjustable contact on the potentiometer and the other end of said resonant circuit and a condenser having low impedance for the resonant high frequency current in said resonant circuit connected between the cathode and said other end of the resonant circuit, the capacity of said condenser being sufliciently low to permit the voltage thereacross to vary in response to modulations on the carrier.

2. In combination in a modulation indicator, a cathode, grid and anode, a visual voltage indicator comprising a source of electrons, and a plate coated on its surface facing said source with a fluorescent substance responsive to electron bombardment, a resonant circuit in series with a radio frequency condenser connected between said grid and said cathode, said condenser being adapted to be charged to substantially the peak value of high frequency voltage across said resonant circuit and to Vary the bias of said grid in response to signal modulations on a carrier wave in the resonant circuit, an antenna coupled to said resonant circuit, an anode circuit including a resistance, and means coupling said resistance to said visual indicator for changing the light" pattern on said plate in response to changes in current in the anode circuit, the size of said light pattern varying with signal changes of said high frequency voltage to indicate percentage modu-" lation.

3. In combination a cathode, grid and anode,

in series between said cathode and anode, a resonant carrier frequency circuit coupled between said grid and said cathode, an antenna coupled to said resonant circuit, a high frequency condenser in the grid circuit for biasing said grid in response to alternating current impressed upon said resonant circuit and for varying the grid bias in response to signal variations of said current, and means for visually indicating the amplitude of direct current flowing in the anode circuit comprising an electron source, a coated plate responsive to electron bombardment to visibly glow, and a deflection electrode between said source and plate, and connections between the ends of said resistance and the deflection electrode and coated plate for deflecting electrons to vary the bombarded area and visually indicate the amplitude of said current and its percentage modulation. JOHN L. REINARTZ. 

